Isolate rich text notifications from other input changes

The step that would notify parent components of rich text state changes was
stirred into the input's change handler, which leads to race which the parent is
sometimes notified of the old rich text state instead of the new.

Here we avoid this complication by using a separate path for sending the rich
text state when we know we have updated it correctly.

src/components/views/rooms/MessageComposer.js

@@ -257,6 +257,8 @@ export default class MessageComposer extends React.Component {
     }
 
     onInputStateChanged(inputState) {
+        // Merge the new input state with old to support partial updates
+        inputState = Object.assign({}, this.state.inputState, inputState);
         this.setState({inputState});
     }
 

src/components/views/rooms/MessageComposerInput.js

@@ -628,7 +628,6 @@ export default class MessageComposerInput extends React.Component {
             }
             const inputState = {
                 marks: editorState.activeMarks,
-                isRichTextEnabled: this.state.isRichTextEnabled,
                 blockType,
             };
             this.props.onInputStateChanged(inputState);
@@ -698,8 +697,13 @@ export default class MessageComposerInput extends React.Component {
         this.setState({
             editorState: this.createEditorState(enabled, editorState),
             isRichTextEnabled: enabled,
-        }, ()=>{
+        }, () => {
             this._editor.focus();
+            if (this.props.onInputStateChanged) {
+                this.props.onInputStateChanged({
+                    isRichTextEnabled: enabled,
+                });
+            }
         });
 
         SettingsStore.setValue("MessageComposerInput.isRichTextEnabled", null, SettingLevel.ACCOUNT, enabled);